Normally, during sausage production filling machines are used, the hoppers of which are open at the top. Here, the sausage meat situated in the hopper is transported to the center by a circumferential feeder curve. In the conveying mechanism located at the outlet of the hopper a negative pressure is produced by a vacuum pump in order to extract air and thus also oxygen from the sausage meat, so that the shelf life of the sausage is extended. On the other hand, a pressure difference Δp to the surface of the hopper charge arises in the conveying mechanism due to the negative pressure such that the paste mass is pressed into the conveying mechanism chamber by the atmospheric air pressure.
The evacuation of the sausage meat can only take place to a restricted extent using this method. In order to extract more air and thus oxygen from the sausage meat, closed hoppers are employed, so-called vacuum hoppers, wherein a negative pressure is produced already in the hopper. Through the negative pressure the paste mass to be charged is pressed out of a reservoir by the higher pressure prevailing there into the closed hopper. Alternatively, the charging of the vacuum hopper can also take place under pressure with an additional pump. During and after the mass has flown into the closed evacuated hopper, air content near to the surface, such as for example air bubbles, are opened up and drawn off from the paste filling mass, i.e. a certain evacuation of the inflowing mass occurs.
The filling level in the hopper is here normally acquired using a level sensor. Depending on the filling level the valve on the feed tube is opened or closed (two-step control). The purpose of this control is solely the level control of the hopper content.
However, the known techniques exhibit the disadvantage that the inflow of the mass takes place more or less abruptly and uncontrollably. Also, the degree of evacuation of the inflowing mass is not optimal due to the principle, because the air content in the mass remote from the surface remains.